1. Field of Invention
The present invention relates to a method and apparatus for automatically detecting the approximate percentage humidity in predetermined types of lumber cut to specific lengths by weighing the lumber and analyzing information signals representative of specific characteristics of a piece of lumber and comparing it with one or more reference signals.
2. Description of Prior Art
There are many governmental and other regulations that demand that lumber be dried before it is utilized in a structure. The humidity in wood varies extensively in accordance with the regions where the trees are grown, the sap in the wood (i.e., pine, spruce, cedar), the nature of the soil where the tree grows, the proximity of the roots of the tree in relation to the water table, etc. All these factors affect the percentage humidity in lumber and cause resulting problems when the lumber is dried. In order to sufficiently dry lumber pieces that are very humid, the drying time of lots of such lumber is relatively long. The disadvantage of such long periods of drying is that the cost for drying the lumber increases as well as the heat loss of the drier. Also, the availability of the drier diminishes. A further disadvantage is that in a lot of lumber there are usually lumber pieces which are substantially less humid than others and therefore these are over dried causing these lumber pieces to twist and/or split, particularly in the ends thereof. Accordingly, this wood becomes inferior in quality and must be removed from the lot and sold at an inferior price. Also, the lumber needs to be reclassified resulting in extra labor costs.
The density of lumber and its weight for a given volume varies in two ways. Firstly, the density of the lumber varies depending on the type of sap in the wood or the wood type, and the density also varies according to the humidity or the water content of the lumber. It is also known that the variations due to the sap density in lumber varies in the order of 25 to 35% of the base weight of the lumber, and that the variations in the weight caused by humidity (water content) could be in the range of 30 to 170%. Since there is more variation in weight caused by humidity, the present invention has concerned itself with determining the humidity in the wood as a criteria for classification of the lumber prior to the drying of same.